<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>

</head>

<body>
  <div id="app">
    <button @click="add">新增arr</button>
    <ul id="oul">
      <li v-for="item in arr">
        {{item}}
      </li>
    </ul>
  
  </div>
  <script src="./vue.global.js"></script>
  <script>
    const { createApp } = Vue;
    const app = createApp({
      data() {
        return {
          arr: [1,2,3,4]
        }
      },
      watch: {
        // 深度侦听
        arr: {
          handler(val){
           
            const oul = document.querySelector('#oul');
            console.log(oul.children);
          },
          deep: true,
          flush: 'post' // 让侦听器触发时机 改为数据修改后且视图更新完成后
        }
      },
      methods: {
        add() {
          this.arr.push(this.arr.length+1)
        }
      },
    })
    app.mount('#app')
  </script>
</body>

</html>